Acid copper plating bath



ACID COPPER PLATING BATH Fred I. Nobel, North Valley Stream, and Barnet D. Ostrow, North Bellmore, N. Y., assignors to Elechem Corp., Jersey City, N. J., a corporation of New Jersey N Drawing. Application July 2, 1%4,

Serial No. 441,652

Claims. (Cl. 204-52 The present invention is directed to acid copper plating baths, more particularly to a bath which is adapted to give improved plating characteristics in operation. I

In recent years, it has been attempted to provide bright plated coatings or deposits of various metals in order to effect economies in the labor necessary for polishing the coatings. This is particularly the case in the plating of automotive parts with copper, nickel and chromium, which are deposited on the ferrous metal successively. Such deposits reproduced the imperfections in the basis metal and considerable prepolishing of the basis metal or copper deposit was necessary before the final nickel and chromium coatings were deposited. Efforts have been made to develop plating baths which not only produce bright deposits but which also reduce the roughness of the final coating. Numerous such attempts have been made and many types of compounds have been added tothe bath, but none of them were capable of giving adequate results.- The principal attempts are set forth below. For instance, coumarin has been added to nickel plating baths, butit is not stable under usual plating conditions, the effectiveness is lost and periodic filtration of the bath becomes necessary. 1 I

For acid copper baths, such additional agents as gelatin, glue and phenol sulphonic acid have been proposed. When phenol sulphonic acid was used it did not produce bright deposits and the deposit was much harder than that obtained without such an addition. The additions of gelatin or glue were of value only in giving grain refinement but they did not produce soft bright deposits; not only did they give hard deposits, but they tended to promote a columnar structure in the deposit. Also the results were variable depending on the source thereof. Glycine has been added to the bath but it was even less effective than gelatin or glue and it had all the disadvantages thereof. 4

Among other additives which have been proposed were peptone, pyrogallol', starch, urea, dimethylaniline, lactic acid, gum arabic, gum trag'acanth, hydroquinon'e, sulphosalicylic acid, hydroxylamine, benzoic acid, tannin, resorcinol, triisopropanolarnine and triethanolamine. These materials in acid copper baths did not give bright deposits. The colloids particularly gave hard, commercially valueless coatings.

Still other substances have been proposed, such as thiourea, thiourea and molasses, thiourea and napthylamine disulphonic acid and cadmium or nickel salts. Since it is desirable to operate acid copper baths at temperatures above 100 F. inorder to obtain higher current densities, as the operable current density range increases with increase in temperature, and since sulphuric acid concentrations of 45 to 110 grams per liter are necessary for successful operation of the bath, thiourea is undesirable because it hydrolyzes in acid solution and-the rate of hydrolysis increases with higher acidityandhigher temperature. Furthermore, thiourea breaks down in the bath and toretard this breakdown, it b e c, omesnecessary to operate at lower temperatures than the optimum.

Also the products of the decomposition are harmful to the bath, making frequent treatment with carbon necessary to remove said products. To operate with lower acid concentrations is not feasible as the conductivity of the bath is reduced as well as the anode and cathode polarization. It has been proposed to add derivatives such as acetyl thiourea but the same disadvantages are inherent therein.

Acetyl cyanamides have also-been proposed but these compounds presentthe same inherent ditficulties as thiourea. 7 They hydrolyze to acetyl urea and baths containing them must be operated at lower temperatures in an elfort to retard breakdown of the additive.

The use of sulphurized aromatic compounds, such as toluene has been proposed, but as far as is known no commercially operable bath has been successfully run. Brighteners of this type are difficult and expensive to manufacture and the baths were diflicult to control.

Aminothiazole and compounds thereof, such as 6-.v

amino-2-mercapto-benzothiazole, "have been, proposed. Although they are more stable than most of the other proposed additions, they have the disadvantage of not increasing the throwing power of the baths, do not give suiiiciently bright deposits, and they do not increase the power of the bath to level or reduce surface roughness. It has been proposed to add glycine in addition to the aminothiazoles to increase the brightness of the deposit. However, in such case the hardness of the deposit increased greatly and the ductility is reduced. Glycine being of the same nature as glue, also tends to break down.

The present invention is intended and adapted to avoid the difficulties and disadvantages inherent in prior acid copper baths which contain additives, it beingamong the objects of the invention to provide a bath of the character described which is capable of giving bright, soft, ductile copper deposits.

It is also among the objects of the invention to provide a bath giving deposits which will be smoother than the basis metal.

It is further among the objects of the invention to incorporate in the baths additives whichare stable over wideranges of acidity and temperature and are highly effective. v

It is still further among the objects of the invention'to provide an additive to the bath which will impart better throwing power and is capable of operation at higher temperature than previously used additives. Y t

In practicing the present invention, there isadded to the acid copper bath any one of three groups of substances, or a combination of any two thereof or of all three. The usual bath is used, for instance of the following compo: sitions:

Copper sulphate (5H2O) -250 gL/l. Conc. sulphuric acid 45-110 g./l.

The first group of substances consists of dialdehydes. To such a bath there is added a very small amount of a brightener which is a dialdehyde of the formula XR: (CHO)2 wherein R represents alkyl having 0 to 10 carbon atoms and aryl, such. as phenyl, and X represents OH and H. Such compounds impart better throwing power to the bath and they refine the structure of the alkyl radical has 1 to carbon atoms, with aminothiazele having the following structural formula:

H QINH:

or with amino-thiazoline having the following structural formula:

0.12 mol of amino-thiazole are mixed with 0.18 mol or glyoxal and the mixture is heated on a water bath at 180-200 F. for about two hours. The color changes as the reaction proceeds from a pale yellow liquid to a dark brown viscous resin having the odor of burnt sugar. The resulting resin is very soluble in 50% sulphuric acid solution and it is dissolved in a mixture of 800 gms. sulphuric acid and 800 gms. water, after which it is diluted with water to one gallon. The product is used in amounts from .01 to 5.0% by volume in the bath. The molar ratio of amino-thiazole to aldehyde may be varied from 1--1 to 1.10, but the best results are obtained at a molar ratio of about 11.5, and added to the bath in amount of about 0.8%, by volume as prepared above.

Example 2 0.1 mol of amino-thiazole are mixed with 0.25 mol of formaldehyde and the mixture is heated on the water bath with the application of a reflux condenser to return volatilized formaldehyde to the mixture, and heating is continued until the reaction is complete. The product is dissolved as set forth in Example 1, and it is added to the plating bath in the amount of about 1.5% by volume.

Example 3 0.1 mol of amino-thiazole are mixed with 0.1 mol of adipaldehyde and the reaction is caused to proceed as described in Example 1. The dissolved and diluted prodnot is added to the plating bath in the amount of about 0.5% by volume.

Example 4 0.1 mol of amino-thiazoline are mixed with 0.2 mol of glyoxal and the resin forming reaction is caused to proceed in accordance with the above examples. The final product is introduced into the "bath in the amount of about 0.6% by volume.

The products of the above two groups may be used in the bath separately or they may be mixed for better results. They impart grain refinement and ductility to the product, and they improve the covering power of the bath. Those of the first group are used in a concentration of .01 gm./l. up to about 20 gms./ l. or to their limit of solubility. For instance, glyoxal may be used in these proportions with optimum results at about 2.5 g1ns./l. The resins of the second group are used in concentrations of 0.001 gms./l. to about 1.0 gm./l. with the optimum range of 0.01 to 0.10 gm./l. giving better-results than the compounds of the first group.

The third group of additives consists of thiazolidincs, thiazolidinethione's and thiazolidinedione's having the following structural formula:

4 wherein Y represents S, 0, COOH, NH: and H, and X represents S and 0.

These compounds, and particularly the thiazolidinethiones, are eifective when used alone in concentrations of 0.001 to 0.10 gm./l. But better results from the standpoint of ductility and brightness level of the deposit are obtained when they are used in conjunction with compounds of the first or second groups, particularly of the second group. For instance, when thiazolidinethions is mixed with a resin formed from glyoxal and aminot'niazole and used in an acid copper bath to deposit 0.001" of copper, the RMS of the surface is reduced from 35 to 10 pin.

The following are examples of baths made in accordance with the present invention:

Example 5 The bath consists of the following constituents in grams per liter of solution:

Copper sulphate (SHzO) 240 Gone. sulphuric acid 74 Glyoxal-aminothiazole resin 0.07 2-thiazolidinethione 0.004

The bath is run at a temperature of 105 F. with air agitation at a current density of 5-150 amps/sq. ft. A deposit of copper of 0.001" obtained at 70 amps/sq. ft. is bright, reduces the surface roughness from 35 to 15 4 in. The brightener is completely stable and the solution can be boiled or it can be stored for extended periods of time and restarted, giving the same excellent results that it gave initially.

Example 6 The bath has the following composition in grams per liter:

Copper sulphate (SHzO) 250 Cone. sulphuric acid 60 Amino-thiazole adipaldehyde resin 0.1 2-thiazolidinethione 0.008

The temperature of the bath during plating is 100 F. and the other conditions are as set forth in Example 5. The results are equally favorable.

Example 7 The following bath is provided: Copper sulphate (SHzO) 250 Conc. sulphuric acid 60 Glyoxal 1.2

The temperature of the bath is F. and the deposit is smooth and ductile over the range of current densities used from 5 to 150 amps/sq. ft.

Example 8 The bath has the following composition: Copper sulphate (SHzO) 240 Cone. sulphuric acid 74 Glyoxal-aminothiazole resin 1.2

A temperature of 110 F. is used over a wide range of current densities, the deposits being smooth and ductile.

Example 9 The following bath gives smooth and ductile deposits when used at F.

When the bath is operated at 110 F., excellent platings are obtained.-'- v Example 11 The bath has the following composition:

Copper fluoborate 224 Fluoboric acid '15 Boric acid 15 Amino-thiazoline glyoxal resin 0.10 2-thiazolidinethione 0.04

When operated under the conditions of Example 1, similar results are obtained.

Example 12 The following baths give satisfactory deposits over a wide range of temperatures and current densities.

Copper sulphate (H20) 250 Conc. sulphuric acid 60 Adipaldehyde 1.2 Amino-thiazoline formaldehyde resin 0.08 Thiazolidine dione 0.003

more than one may be used with the same good eflects.

Various compositions of the base acid copper bath, such as have been described in the literature, may be used in conjunction with the present additives. The copper deposit may be of any desired thickness and such thickness may be increased at the expense of the nickel overcoating with equally satisfactory results, thus providing a substantial saving in cost of metal due to the much lower cost of the copper.

We claim:

1. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and amino-thiazoline with a substance taken from the class consisting of alkyl aldehydes, aryl dialdehydes and alkyl dialdehydes wherein the alkyl groups have from 1 to carbon atoms, the amount of said addition being suflicient to impart brightness and ductility to deposits of copper from said bath.

2. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and amino-thiazoline with glyoxal, the amount of said addition being suiticient to impart brightness and ductility to deposits of copper from said bath.

3. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and amino-thiazoline with formaledhyde, the amount of said addition being sufficient to impart brightness and ductility to deposits of copper from said bath.

4. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and amino-thiazoline with adipaldehyde, the amount of said addition being sufiicient to impart brightness and ductilit'y'to' deposits of copper from said bath.

5. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and amin'orthiaz'oline with a substance taken from the class consisting of alkyl aldehydes and alkyl dialdehydes wherein the alkyl groups have from 1 to 10 carbon atoms, together with an alkyl dialdehyde wherein the alkyl group has from 0 to 10 carbon atoms, the amount of said addition being sutficient to impart brightness and ductility to deposits of copper from said bath.

6. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and aminothiazoline with a substance taken from the class consisting of alkyl aldehydes and alkyl dialdehydes wherein the alkyl groups have from 1 to 10 carbon atoms, together with glyoxal, the amount of said addition being sufficient to impart brightness and ductility to deposits of copper from said bath.

7. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and amino-thiazoline with a substance taken from the class consisting of alkyl aldehydes and alkyl dialdehydes wherein the alkyl groups have from 1 to 10 carbon atoms, together with adipaldehyde, the amount of said addition being sufiicient to impart brightness and ductility to deposits of copper from said bath.

8. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and amino-thiazoline with a substance taken from the class consisting of alkyl aldehydes and alkyl dialdehydes wherein the alkyl groups have from 1 to 10 carbon atoms, together with a substance taken from the class consisting of thiazolidines, thiazolidinethiones, and thiazolidine diones, the amount of said addition being suflicient to impart brightness and ductility to deposits of copper from said bath.

9. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvementwhich includes the addition to said bath of the resinous reaction product obtained by the heating together up to about 200 F. of a substance taken from the class consisting of amino-thiazole and amino-thiazoline with a substance taken from the class consisting of alkyl aldehydes and alkyl dialdehydes wherein the alkyl groups have from 1 to 10 carbon atoms, together with a substance having the following structural formula:

where Y represents a member selected from the group consisting of S, 0, COOH, NHz and H, and X represents a member selected from the group consisting of S and O, the amount of said addition being sufiicient to impart brightness and ductility to deposits of copper from said bath.

10. In an acid copper plating bath containing a salt of copper and a free acid as the essential constituents, the improvement which includes the addition to said bath of the resinous 'caction product obtained by the heating together up to about 200 F. of 2. Substance taken from the class consisting of amino-thiajzole and amino-thiazoline with a substance taken from the class consisting of alkyl aldehydes and alkyl dialdehydes wherein the alkyl groups have from 1 to 10 carbon atoms, together with an alkyl dialdehyde wherein the alkyl group has from O to 10 carbon atoms, and including a substance taken iron; the class consisting of thiazolines, thiazolidinethiones and thiazolidine diones, the amount of said addition being sufficient to impart brightness and ductility to deposi's'ts of copper from said bath.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN AN ACID COPPER PLATING BATH CONTAINING A SALT OF COPPER AND A FREE ACID AS THE ESSENTIAL CONSTITUENTS, THE IMPROVEMENT WHICH INCLUDES THE ADDITION TO SAID BATH OF THE RESINOUS REACTION PRODUCT OBTAINED BY THE HEATING TOGETHER UP TO ABOUT 200* F. OF A SUBSTANCE TAKEN FROM THE CLASS CONSISTING OF AMINO-THIAZOLE AND AMINO-THIAZOLINE WITH A SUBSTANCE TAKEN FROM THE CLASS CONSISTING OF ALKYL ALDEHYDES, ARYL DIALDEHYDES AND ALKYL DIALDEHYDES WHEREIN THE ALKYL GROUPS HAVE FROM 1 TO 10 CARBON ATOMS, THE AMOUNT OF SAID ADDITION BEING SUFFICIENT TO IMPART BRIGHTNESS AND DUCTILITY TO DEPOSITS OF COPPER FROM SAID BATH. 